A method for determining rock mass properties is described in: V. N. Dakhnov Promyslovaya Geofizika (Production Geophysisc), Moscow, Gostopizdat, 1959, pp. 56-59. This method comprises measuring temperature distribution along a borehole drilled in a rock mass after a thermal disturbance of the rock mass by circulating a fluid with temperature different from temperature of the rock mass and subsequent identification of zones of productive layers with different properties. In this case the zones of the productive layers are identified by a difference between temperature in the zones of the productive layers and temperature of non-productive areas after the circulation. A disadvantage of this method is the difficulty in identifying the zones of the productive layers when these zones are separated from the borehole by layers with invasion of the circulation fluid due to the impossibility to record small temperature drops between the zones of the productive layers and the non-productive areas against the background of large absolute values of temperature typical for the rock mass at oil occurrence depths. Another disadvantage of this method is the fact that the temperature in the borehole is recorded after circulation of the fluid in the borehole when a temperature profile at the boundaries of the layers of the rock mass with different properties is blurred due to conductive heat transfer process between the rock mass sections with different temperature. Yet another disadvantage of this method is the fact that the time period during which the borehole temperature profile should be recorded is not defined which reduces the efficiency of the method. One more disadvantage is the impossibility to measure the rock mass temperature as a function of time at each selected depth which also reduces the sensitivity of the method because it does not enable differentiation between effect of a noise and effect of rock mass properties on temperature changes in time.
An apparatus for studying properties of rock mass is described in: V. N. Dakhnov Promyslovaya Geofizika (Production Geophysisc), Moscow, Gostopizdat, 1959, pp. 56-59. The apparatus comprises a circulation fluid supply unit, a temperature sensor, an electronic unit to record and process a temperature signal, a cylindrical enclosure in which the temperature sensor, the electronic unit, a cable to run the cylindrical enclosure into the well, to transmit the supply voltage and to transmit measurement results to the surface are located. The apparatus is used for the implementation of the above method of studying rock mass properties. A disadvantage of this apparatus is the impossibility to record the borehole temperature distribution during the circulation of the fluid which results, as mentioned before, in extended measurement time, indistinct identification of boundaries of the rock mass layers with different properties. Another disadvantage is the presence of only one temperature sensor which results in the insufficient sensitivity of determining properties of the rock mass when layers with low difference in their properties are identified.